Field of the Invention
The invention relates to a pump for conveying a highly viscous fluid.
Background of the Invention
Pumps for pumping highly viscous fluids are used in many different industries, for example in the oil and gas processing industry for conveying hydrocarbon fluids. Here, these pumps are used for different applications such as extracting the crude oil from the oil field, transportation of the oil or other hydrocarbon fluids through pipelines or within refineries. But also in other industries, for example, in the food industry or the chemical industry there is often the need for conveying highly viscous fluids.
The viscosity of a fluid is a measure for the internal friction generated in a flowing fluid and a characteristic property of the fluid. Within the framework of this application the term “viscosity” or “viscous” is used to designate the kinematic viscosity of the fluid and the term “highly viscous fluid” shall be understood such, that the fluid has a kinematic viscosity of at least 10−4 m2/s, which is 100 centistokes (cSt).
For the pumping of highly viscous fluids it is known to utilize centrifugal pumps. Pumping highly viscous fluids with centrifugal pumps requires considerably more pump power than for example pumping water. The higher the viscosity of the fluid becomes the more power the pump needs to deliver the required pumping volume. Especially in the oil and gas industry the main focus—at least in the past—has been on pumping volume, i.e. the flow generated by the pump, and on the reliability of the pump rather than the efficiency of the pump. However, nowadays a more efficient use of the pump is strived for. It is desirable to have the highest possible ratio of the power, especially the hydraulic power, delivered by the pump to the power needed for driving the pump. This desire is mainly based upon an increased awareness of environment protection and a responsible dealing with the available resources as well as on the increasing costs of energy.
To improve the efficiency of a pump for pumping highly viscous fluids it is known to use specific impeller designs, especially impellers with high head coefficients. The head coefficient of the impeller can be increased for example by increasing the blade outlet angle or the number of blades or the impeller outlet width. Despite of these measures there is still a need to even more improve the efficiency of a pump for pumping highly viscous fluids.